In the last grant period this laboratory was able to play a major role in the discovery that the amino terminus common to all T antigens in the SV40/polyoma family of viruses is a functional dnaJ domain. This discovery, which was the work of a group of labs in the papova virus field, stands as a milestone in the study of these viruses. The viral J domain "function" plays a role in viral replication, regulation of the host cell cycle, and transformation. It is possible that the J domain may underlie other viral processes such as virus assembly as well. It is now time to bring our studies of the J domain to a more mechanistic level. In the coming grant period the molecular mechanisms by which the J domain of SV40 virus enhances DNA replication and frees the E2F complex from inhibition by the Rb family of tumor suppressor proteins will be elucidated.